1. Field of the Invention
The invention relates to a fuel injection valve.
2. Description of the Related Art
A fuel injection valve for a compression ignition internal combustion engine 1′ as shown in FIG. 11A, FIG. 11B, FIG. 12A, and FIG. 12B is known. In this fuel injection valve 1′, a nozzle chamber 5′, and a coil chamber 6′ are formed in a housing 2′. A sack 7′ is formed at a bottom end of the nozzle chamber 5′. A nozzle 8′ is provided in a peripheral surface of the sack 7′. The coil chamber 6′ is connected to a top end of the nozzle chamber 5′ through a slide portion 9′. A needle 10′ extends from the nozzle chamber 5′ to the coil chamber 6′ through the slide portion 9′. The needle 10′ is slidably supported in the slide portion 9′.
The nozzle chamber 5′ is connected to a common rail (not shown) through a fuel port 14′. The coil chamber 6′ is connected to the nozzle chamber 5′ through a pressurized fuel supply passage 15′. These nozzle chamber 5′ and the coil chamber 6′ are filled with pressurized fuel. A solenoid coil 11′ and a fixed core 12′ are fixed in the coil chamber 6′. An armature 13′ is formed on the needle 10′ at a portion positioned in the coil chamber 6′ such that the armature 13′ is opposed to the solenoid coil 11′. A compression spring 24′ is inserted between an inner wall surface of the housing and an outer surface of the needle. The compression spring 24′ applies force to the needle 10′ in a valve closing direction.
Particularly as apparent from FIG. 11B, a needle seat 16′ is formed in an inner wall surface of a nozzle holder 3′ adjacent to the sack 7′. When the needle 10′ is seated at the needle seat 16′, an annular seal 17′ is formed between the needle 10′ and the needle seat 16′.
As shown as a projection plane at a bottom of FIG. 11B, a downward pressure receiving surface 21′ is formed in the needle 10′ at a portion positioned in the nozzle chamber 5′. The downward pressure receiving surface 21′ includes a downward pressure receiving surface outer portion 21a′ and a downward pressure receiving surface inner portion 21b. The downward pressure receiving surface outer portion 21a′ is an annular portion on a radially outer side of the aforementioned annular seal 17′. The downward pressure receiving surface inner portion 21b′ is a portion on an inner side of the downward pressure receiving surface outer portion 21a′ and the annular seal 17′. Meanwhile, an upward pressure receiving surface 23′ is formed in the needle 10′ at a portion positioned in the coil chamber 6′. The upward pressure receiving surface 23′ is shown also as a projection plane at a top portion of FIG. 11B.
Each of FIG. 11A and FIG. 11B shows the fuel injection valve 1′ when closed. In this case, the solenoid coil 11′ is de-energized. The needle 10′ remains seated in the needle seat 16′, whereby fuel injection is stopped.
When fuel injection should be started, the solenoid coil 11′ is energized. As a result, upward magnetic attraction force of the solenoid coil 11′ is applied to the needle 10′, and the needle 10′ is displaced upward, and is separated from the needle seat 16′. Then, fuel injection is started. Subsequently, when the armature 13′ hits a bottom end surface of the fixed core 12′, upward displacement of the needle 10′ is restricted.
When the fuel injection should be stopped, the solenoid coil 11′ is de-energized. As a result, the needle 10′ is displaced downward by spring force of the compression spring 24′. Subsequently, when the needle 10′ is seated at the needle seat 16′ as shown in FIG. 11A and FIG. 11B, the fuel injection is stopped.
When the fuel injection is stopped as shown in FIG. 11A and FIG. 11B, downward pressure of pressurized fuel is applied to the upward pressure receiving surface 23′, upward pressure of pressurized fuel is applied to the downward pressure receiving surface outer portion 21a′, and the pressure of pressurized fuel is not applied to the downward pressure receiving surface inner portion 21b′, as shown by hatcing in FIG. 12A. When the solenoid coil 11′ is energized, the upward magnetic attraction force is applied to the needle 10′. Accordingly, in this case, the solenoid coil 11′ is required to supply the magnetic attraction force such that the needle 10′ is separated from the needle seat 16′ by the upward magnetic attraction force of the solenoid coil 11′ and the upward force applied to the downward pressure receiving surface outer portion 21a′, against the downward force applied to the upward pressure receiving surface 23′ and the downward spring force of the compression spring 24′.
When the needle 10′ is separated from the needle seat 16′, the upward pressure of pressurized fuel is applied not only to the downward pressure receiving surface outer portion 21a′ but also to the downward pressure receiving surface inner portion 21b′, as shown by hatching in FIG. 12B. Subsequently, when the solenoid 11′ is de-energized, the upward magnetic attraction force is no longer applied to the needle 10′. Accordingly, in this case, the compression spring 24′ is required to supply the spring force such that the needle 10′ is displaced downward to the needle seat 16′ by the downward force applied to the upward pressure receiving surface 23′ and the downward spring force of the compression spring 24′, against the upward force applied to the downward pressure receiving surface outer portion 21a′ and the upward force applied to the downward pressure receiving surface inner portion 21b′. 
In the aforementioned fuel injection valve, when the needle 10′ is separated from the needle seat 16′, an area of the pressure receiving surface to which the upward pressure of pressurized fuel is applied is increased by an area of the downward pressure receiving surface inner portion 21b′, as compared to when the needle 10′ is seated at the needle seat 16′. Accordingly, as apparent from the aforementioned requirement for the compression spring 24′, the spring force of the compression spring 24′ needs to be increased. Therefore, as apparent from the aforementioned requirement for the solenoid coil 11′, the magnetic attraction force of the solenoid coil 11′ needs to be increased. This signifies that an amount of energy consumed by the solenoid coil 11′ becomes extremely large, or size of the solenoid coil 11′ becomes large.